1. Field of the Invention
The present invention relates to an implantable heart monitoring device of the type having a control circuit and a memory connected to the control circuit. The control circuit is in communication with one or more sensor members suitable to be positioned in or at the heart of a living being. The control circuit is also arranged to at least enable the following: based on signals, received from the one or more sensor members, derive a first value, related to the volume of a first part of the heart, and, based on signals, received from the one or more sensor members, derive a second value, related to the volume of a second part of the heart. The invention also relates to a system including such a device and to the use of the system. The device may be used to monitor the performance of a heart of a human or animal being, and also to deliver stimulation pulses to the heart.
2. Description of the Prior Art
Several different devices for monitoring the performance of a heart are known. Often these devices are also able to deliver stimulation pulses to the heart. The devices are often able to sense the electrical activity of the heart. It is also known to sense an impedance value measured between different electrodes positioned in the heart. It is also known to sense other physiological parameters, such as pressure, oxygen level etc.
U.S. Pat. No. 6,070,100 describes that electrodes may be positioned in both the left and the right atrium as well as in or at the left and the right ventricles. The document describes the possibility of sensing the impedance between different electrodes. The sensed impedance values may be used to improve the cardiac output.
U.S. Pat. No. 5,720,768 describes different possible electrode positions in order to stimulate or sense the different chambers of the heart.
U.S. Pat. No. 5,154,171 describes the sensing of impedance values in order to control the pacing rate.
U.S. Pat. No. 6,604,002 describes different manners of using the proximal and distal electrodes of different leads in order to inject a current and to measure an impedance. The measured impedance value may be used in order to maximize the cardiac flow.
U.S. Pat. No. 6,556,866 describes bi-ventricular pacing. An impedance may be measured between electrodes on the right and the left sides of the heart. The variation of the impedance with time is detected. The detected impedance variation may be used in order to synchronize the contraction of the ventricles.
U.S. Pat. No. 6,280,389 describes a bi-ventricular pacer. Pressure is sensed in the right and left ventricles. A graph showing the relation between left ventricular pressure and right ventricular pressure during a heart beat is formed. This graph will form a loop. The heart performance is related to the area within this loop.
The variation in pressure between the two ventricles, as described in the above mentioned document U.S. Pat. No. 6,280,389, is not always the best measure for analyzing the performance of the heart and, consequently, not always the best basis for controlling the delivery of pacing pulses in order to optimize the performance of the heart. Furthermore, it can be difficult to measure the pressure, in particular in the left ventricle.